In October 1998 a conference was held in Lisbon to celebrate the 60th birthday of Ludwig Streit. This volume collects some of the papers presented at the conference as well as other essays contributed by the many friends and collaborators who wanted to honour Ludwig Streit's scientific career and personality. The contributors cover many aspects of contemporary mathematical physics. Of particular importance were new results on infinite-dimensional stochastic analysis and its applications to a wide range of physical domains.